The present invention relates to a new electronic weft or filling thread monitoring device for shuttleless looms or weaving machines, such as gripper shuttle and rapier weaving machines. Generally, such a monitoring device serves for stopping the loom as soon as the weft thread breaks or is prematurely released from the gripper member during insertion into the weaving shed.
A gripper shuttle weaving machine provided with an optical weft thread monitoring apparatus is shown and described in U.S. Pat. No. 3,489,910, by way of example. Swiss Pat. No. 489,642 discloses a device for monitoring the weft thread on gripper shuttle weaving machines, said device comprising a preferably weft contacting sensor arranged on the picking side of the machine between supply spool and weaving shed, and circuitry determining a monitoring interval in which part of the weft insertion period is supervised. Such circuitry comprises a control member located near the end of the gripper shuttle race and producing a control pulse determining the end of the monitoring interval when the gripper shuttle passes the control member. The latter may be mounted near or within a gripper shuttle catch box. Preferably this control device is arranged ahead of the catch box since its mounting within the same is not possible without engineering changes and thus is not generally practicable. However, with such preferred arrangement, the control pulse appears so early that the monitoring interval is terminated prior to the stoppage of the gripper shuttle and weft or filling thread. As a consequence, the thread is no longer monitored during the last phase of its travel, i.e. after the gripper shuttle has passed the control device. This last phase may comprise a time interval of ten milliseconds or more. Now in order to reduce this non-monitored time interval, the control or controlling pulse, as disclosed in the aforementioned Swiss patent, may be delayed by a constant amount such that the monitoring interval is prolonged by the same amount.
However, the duration of such last phase of the filling insertion period depends upon the type of weaving machine, the adjustment and the working conditions thereof, and in particular the type of filling yarn. Thus it is desirable that the amount of such time delay should be fixed according to circumstances. By way of example, the optimal delay may be in the range from six to twelve milliseconds. The delay may be set by shifting and adjusting the control device generating a controlling pulse along the path of the gripper shuttle. However, such measure requires additional expenditure of mechanical means and, moreover, generally is impracticable due to lack of space. Furthermore, special measuring equipment is required for checking the correct setting, so that only trained personnel is able to perform the setting.